By the application of the air permeability method to the specific surface measurement of materials ground in a steel ball mill the energy required for grinding and the new surface produced has been established for base materials (pitch cokes), baked and electro-graphitized carbon rod. It has been shown that for these materials the relationship between the energy and new specific surface may be represented by a convex curve (dS/dE>0).
The results were as follows:
Judging from the increase of the specific surface of ground materials only,
(1) the cokes carbonized from binder tend to be ground more easily than the base materials (pitch cokes).
(2) Final value of specific surface (S∞) and comminution coef.(K) were measured. It was found that K was constant for carbons, which was probably fixed according to inner structure and surface characteristics of the carbon.
Final specific surface was discussed from the point of maximum impact stress produced in the pulverized materials.